Deposition of metallic films from metal vaporized in vacuo



NOV. 23, 1937. P, ALEXANDER 2,100,045

DEPOSITION OF' METALLIC FILMS FROM METAL VAPORIZED IN VACUO .Filed Oct.l0, 1936 [NVE/VTM. -PHUL /CL [XH/VDH? @frog/vars Patented Nov. 19237UNITED STATES DEPOSITION OF METALLIC FILMS FROM METAL VAPOBIZED IN VACUOPani Alexander, Brussels, Belgium Application October 10, 1936, SerialNo. 105,091 In Germany October 12. 1935 This invention relates to thedeposition of metallic illms from metal vaporized in vacuo. w In orderto obtain a film which has the characteristics of the metal and adheresiirmly to its support, it has heretofore been found necessary to effectthe vaporization and deposition in an enclosure with high vacuum, of theorder oi 1 10,000 mm. or lower. To obtain and maintain so high a vacuumcommercially presents great difliculties. If a lower vacuum be employed,the lm obtained is subject to some or all of the following defects; itdoes not adhere well, it is porous, its reflecting power is small, itselectrical conductivity is low, it

is dark in color and, by transmitted light shows colors indicating acolloidal state.

According to the invention, films are deposited at substantially higherpressures than 1/ 10,000 mm. which have the characteristics of filmshitherto deposited at this pressure, by heating the metallic vapor inits passage from its source to the support of the lm.

It is believed that the reason why this heating of the vapor iseffective in producing a good illm at higher pressures is thefollowingz-The partial pressure of the metal vapor close to the sourceof evaporation is higher than that of the residual gas in the vacuumchamber. The partial pressure of the metal vapor, however, diminishesrapidly with the distance from the source of evaporation. The metalatoms, in their passage from source to support, lose kinetic energy asthe result oi' collisions with the molecules of the relatively coldresidual gas. Metal atoms ofv low kinetic energy, colliding with eachother, tend to coalesce to form particles of colloidal dimensions,which, when deposited on the support, form a defective film. When,according to the invention, heat is communicated to the metal vapor atan intermediate point of its passage from source to support, kineticenergy is imparted to the atoms, and coalesced particles arereevaporated into atomic form. In the further passage from thisintermediate point to the support, the partial pressure of the metalvapor is much lower than it is from the source to the intermediatepoint, and is low in comparison with that of the residual gas;collisions of the metal atoms are then with gas molecules rather thanwith other metal atoms, and the metal vapor consequently completes thepassage substantially in atomic form and is in this form deposited onthe support.

In the accompanying drawing:-

Figures 1, 2 and 3.are vertical sections through alternative forms ofapparatus for carrying out the invention, shown partly diagrammatically;

Figure 4 is a part section of an alternate form of vapor heating device;

Figure 5 is a section through an alternative form oi' heating vessel,and

Figure 6 is a section through an alternative form o1' heating device forthe metal.

Referring to Figure 1, the vacuum chamber I contains the support 2 onwhich the metal iilm is to be deposited, and the heating vessel 3contains the metal to be vaporized. The supports for the various partsln the chamber are not shown in the drawing. The heating vessel 3 is arefractory tube having holes 4 for the issueof the metal vapor. Thevessel 3 is heated by current passed through the spiral 5 from theconductors 6. Between the heating vessel 3 and the support 2 is a devicefor heating the metal vapor, consisting oi two wire mesh screens 1connected with conductors 8 whereby current is passed through thescreens to heat them to at least the vaporization temperature of themetal to be deposited. The metal vapor issuing from the holes l, passesthrough the meshes of the screens 'l in its passage to the support 2,and is heated by the screens, and is deposited on the support 2 in theform of a lm of good quality.

By means of the vapor heating screens 1, films have been deposited, at achamber pressure of 1/ 100 mm. and even higher, which are of as goodquality as lms heretofore deposited at pressures of 1/10,00Q mm. andlower.

Figure 2 shows an alternative form of heating vessel 3 and analternative form of vapor heating device. The vessel here consists of atube of metal of high melting point, such as tungsten or molybdenum,which itself forms the heating element through which current is passedby the conductors i. The vapor heating device consists of a tube 9 bentin zig-zag, supplied with a gas inert to the metal vapor at its righthand end and closed at its left hand end. The tube 9 may itself form theheating element, as shown in the drawing, current being supplied to itby the conductors 8. In this case, the tube may be made of palladium,and the gas supplied may be hydrogen, to which the walls of the tube areporous. Alternatively, the tube may be made of a porous refractorymaterial, and heated by a spiral wire heating element. The heated gasissuing through thewalls ofthe tube 9 heats the metal vapor in itspassage between the zig-zags of the tube. 'I'he quantity of gasintroduced must not be so large as unduly to increase the vaporizationtemperature of the metal. Even without continuous evacuation, sufficientgas can be introduced to heat the metal vapor effectively current byconductors l (of which one is visible),

Eil

contained in the vessel 3. Above the outlet l2 of the vessel S is ametal plate i3 which-is heated to a temperature at least equal to thevaporization temperature of the metal to be deposited, by current passedthrough it from conductors d (of which one is visible). The metal vaporissuing from the outlet I2 impinges against the heated plate it in itspassage to the support t and is heated thereby.

The heating of the'vapor heating device, such as the wire mesh screen lmay be eilected as shown in Figure 4, in which the screen is in twoparte 'la and 1b insulated one from the other and connected to hightension conductors l, whereby a glow discharge is maintained between theas shown in Figure 6, where the metal l0 is contained in a refractoryvessel 3, while above it are located plates l5; the plates i5 and themetall it are connected to high tension conductors it, whereby a glowdischarge is maintained between the plates and the metal.

It is of advantage, in order that the partial pressure of the metalvapor may be kept low, that its concentration at its point of issuei'rom the heating vessel be as low as'possible. For this purpose aheating vessel such as that shown in cross-section in Figure 5 is ofadvantage, in which the cross-sectional area (that is to say, the spacefor the vapor) increases from the surface lil of the metal to the outletIll.

Another device for diminishing the concentra.-l

porizes at about 609 C., the vapor pressure of tin is negligibly small.

'I'he residual gas in the chamber should be, as

usual, inert with respect to the metal vapor, and

it is oi advantage that it be ionized. Thereby a good nlm is obtained athigher gas pressure or with more rapid vaporization. The ionization maybe produced by electrodes it (Figure 1) within the chamber l, to whichelectric potential is applied.

By means of the invention applicant has produced lms of good qualitywith a gas pressurein the vacuum. chamber exceeding 1/100 mm., but themaximum pressure which can be used depends on the rate of vaporization,the degree of heating of the vapor in its passage to the support, thevapor pressure of the metal used and whether the gas is ionized, and,for any given set of conditions, can best be ascertained by trial.

Having described my invention I declare that what I claim and desire tosecure by Letters Patent isz- 1. Apparatus for depositing a metal filmon a support in an evacuated chamber, comprising means for vaporizingthe metal and means located between the source of the vapor and thesupport adapted to heat the metal vapor.

2. Apparatus for depositing a-metal lm on a support in an evacuatedchamber, comprising means for vapog the metal. a metallic member adaptedto allow the metal vapor to pass through it, interposed between thesource of the vapor and the support, and means for heating the metallicmember to a temperature above the vaporization temperature of the metal.

3. Apparatus for depositing a' metal nlm on a support in an evacuatedchamber, comprising means for vaporiaing the metal. a wire mesh screenvlocated between the source oi' the vapor and the support, and means forheating the wire mesh screen to a temperature above the vaporisationtemperature of the metal.

d. Apparatus ior depositing a metal film on a support in an evacuatedchamber, comprising means for vaporizing the metal, a metallic member solocated that the vapor issuing from the source impinges upon it in thepassage of the vapor to the support, and means for heating the metallicmember to a temperature above the vaporization temperature of the metal.

5. Apparatus for depositing a metal nlm on al support in an evacuatedchamber, comprising means for vaporizing the metal, a metallic memberadapted to allow the metal vapor to pass through it, interposed betweenthe source of the vapor and the support, an electrode, and means forproducing a glow discharge between the metallic member and theelectrode. A

6; Apparatus for depositing a metal nlm on a support in an evacuatedchamber, comprising means for vaporizing the metal, two wire meshscreens located between the source of the vapor and the support andmeans for producing a, glow discharge between the two wire mesh screens.

'7. Apparatus as in claim 1, comprising two electrodes and means forproducing an electric discharge between them adapted to ionize the gasin the chamber.

fr 8. Apparatus as in claim 2, comprising two electrodes and means forproducing an electric discharge between them adapted to ionize tlie gasin the chamber.

9. Apparatus for depositing a metal ilm on a support in .an ,evacuatedchamber, comprising a vessel adapted to contain the metal to bevaporized and means for supplying heat to the metal to vaporize it, thevessel being so shaped that its cross-sectional area increases from thesurface of the metal to the outlet, and means located between the outletand the support adapted to heat the vapor.

10. Apparatus for depositing a metal nlm on a support in an evacuatedchamber, comprising a metallic vessel adapted to contain the metal to bevaporized, means for passing an electric current through the vessel toheat it to a temperature above the vaporization temperature of themetal, and means located between the outlet of the vessel and thesupport adapted to heat the vapor.

11. Apparatus for depositing a metal film on a support in an evacuatedchamber, comprising a vessel adapted to contain the metal to bevaporized, an electrode, means for producing a glow discharge betweenthe metal and the electrode, adapted to heat the metal to vaporize it,and means located between the outlet of the vessel and the supportadapted to heat the vapor.

12. Apparatus as in claim 9, comprising two electrodes and means forproducing an electric discharge between them adapted to ionize the gasin the chamber.

13. Apparatus as in claim 10, comprising two electrodes and means forproducing an electric discharge between them adapted to ionize the gasvin the chamber.

14. Apparatus as in claim 11, comprising two electrodes and means forproducing an electric discharge between them adapted to ionize the gasin the chamber.

15. Process of depositing a metal illm on a support-in an evacuatedchamber, comprising the steps of vaporizing the metal and heating thevapor in its passage from its source to the support.

16. Apparatus for depositing a metal lm on a support in an evacuatedchamber. comprising means for vaporizing the metal, a tubular memberinterposed between the source of the vapor and the support, means forheating the tubular member to a temperature above the vaporizationtemperature oi' the metal and means for supplying into the tubularmember a gas inert to the metal, the walls of the tubular member beingporous to the gas. the rate ot introduction of the gas being so low thatthe vaporization temperature of the'metal is not substantially increasedby reason of rise of pressure in the chamber;

17. Process of depositing ametal illm on a support in an evacuatedchamber, comprising the steps of embodying the metal to be deposited ina comparatively large portion of another metal, having, at the pressureinthe chamber, a. vapor pressure low in comparison with that of themetal to be deposited, heating the combined mass of metal to vaporizethe metal to be deposited, and without appreciably vaporizing the othermetal, heating the vapor in its passage from its source to the support.

18. Apparatus i'or depositing a metal lm on a support in an evacuatedchamber, comprising f means for heating the gas.

19. Apparatus as in claim 18, comprising two electrodes and means forproducing an electric discharge between them adapted to ionize the gasin the chamber.

PAUL ALEXANDER. 2l

